Malleability

Malleability is that property of a material that allows it to be easily shaped. Gold is malleable. Stone is not.

Code should be malleable.

Polymorphism (from the Greek poly meaning "many", and morphe meaning "form, shape") adds to malleability. So do unit tests. Coupling destroys malleability. Cohesion enhances it.

Reluctance to modify code is a sure sign that malleability is being degraded. Attend to it. If it is hard to do now, it is not going to easier on its own.

Code that is not malleable become "Bhoot Banglas". Code that is not malleable is code that is petrified (from the Greek petro for stone). Petrified code leads to petrified code maintainers.